Samsung 16800Mah Power Bank — Not keep charging...

Address:	Dadra and Nagar Haveli, Dadra and Nagar Haveli, 396230
Website:	book my offer

I have buy a power bank of samsung 16800mah from book my offer as reference no.:- [protected].
But it's very weak to keep charging in, only 2 to 3 minutes it's take place. After that it's discharge suddenly.
I had feeling very surprised & frustrate too, can't understand what to do? I have also many times try to call on book my offer customer care help no.:- [protected], but no one picked up phone.
So, please help to return.